Communications systems need a transmission medium for signals that is often formed by multiple conductors. The presence of these multiple conductors can be used to improve different features of the communications system, such as the transmission capacity or noise immunity, among others. Although this problem has been considered and some more or less valid solutions have been found in the past, the present invention presents a new solution which optimally uses the multiplicity of conductors for increasing the performance of the transmission in the medium.
The conventional concepts which are used in the present invention are described below. “Mode” is understood as the injection of voltage or current on a selective combination of conductors, reference plane or both. Likewise, “orthogonal multi-injection” is defined as an injection of multiple modes orthogonal to one another. The injection modes are divided into common mode, differential modes and pseudo-differential modes. The common mode is what causes the circulation of currents through the reference plane. The differential modes consist of the injection through one conductor and the return through another one, whereas the pseudo-differential modes consist of the injection of voltage or current between one or more conductors and the return through one or more conductors different from those used for the injection, the number of conductors used in this case being more than two.
The patent “Space time coded data transmission via inductive effect between adjacent power lines” (GB238372A), describes the use of multiple paths for the communications signal on the electric network and in the digital processing application for identifying in each node the best time periods and frequency for communicating. Furthermore, in this document, the channel is treated as a system of multiple inputs and multiple outputs wherein the signal is coupled between the different conductors to reach the nodes through several paths. This document does not affect the novelty or the inventive step of the present invention, because orthogonal multiple injections are not performed on a multi-conductor medium, but rather a different method is applied to perform the communications which seeks to use the crosstalk between conductors instead of eliminating it.
On the other hand, the publications “A novel approach to the modeling of the indoor power line channel Part I: Circuit analysis and companion model” (IEEE Trans. Power Del., vol. 20, no. 2, pp. 655-663, April 2005) and “A novel approach to the modeling of the indoor power line channel Part II: Transfer function and channel properties” (IEEE Trans. Power Del., vol. 20, no. 3, July 2005) analyze the channel formed by the electric network as a transmission medium in homes, assimilating it to the theory of multi-conductor transmission lines (MTL), for the purpose of achieving a realistic model for said channel. This does not affect the novelty or the inventive step of the present invention because the invention is based on the increase of the performance of a communications system by means of the orthogonal multi-injection of signals, independently of the model used for the channel.
Another publication of the state of the art is entitled “High-Frequency characteristics of overhead multi-conductor power lines for broadband communication” (IEEE Jour. Communications, Vol. 24, no. 7, July 2006), and presents another advanced model for the channel formed by the electric network as a transmission medium in overhead medium voltage transmission lines. For the same reasons indicated above, this document does not affect the novelty or inventive step because the method of the present invention can be applied independently of the modeling performed on the communications channel.
On the other hand, the publication “Characteristics of power line channels in cargo ships” of Tsuzuki, Yoshida, Yamada, Kawasaki, Mrai, Matsuyam and Suzuli (IEEE 1-4244-1090-8/07) describes the manner of characterizing the electric network of the cables of a cargo ship, wherein the wiring is double-stranded with a grounded shield. To that end, one and the same signal is injected in a common and differential manner (dual mode transmission), and it is received in a differential manner, whereby signal conversion by crosstalk is used to achieve less attenuation with respect to the use of only differential transmission. In other words, this publication seeks to have a single communications channel from a system of several strands. The present invention uses orthogonal injection modes in N cables seeking to achieve up to N independent communication channels, using said orthogonality for increasing the performance of a communication system preventing crosstalk instead of enhancing it, which is neither anticipated nor is it an evident result for a person having average skill in the art from this publication.
The state of the art prior to the present patent also includes the publication “Vectored Transmission for Digital Subscriber Line Systems” (George Ginis, John M. Cioffi, IEEE Journal On Selected Areas in Communications, Vol. 20, No. 5, June 2002) in which the manner of increasing the transmission rate in a bundle of twisted pairs is described, wherein the injection in said twisted pairs is done in a differential manner, coordinating the transmissions and using techniques for multiple input and multiple output (MIMO) to cancel the crosstalk. As occurs with other documents of the state of the art, this does not anticipate the present invention the method of which is based on orthogonal injections on N conductors to increase the performance of a communications system.
A patent from the technological background relating to the problems to be resolved is the so-called “Phantom Use in DSL systems” with publication number US 2006/0268966. This patent uses a common mode which is superimposed on the signals which are sent in a bundle of twisted pairs (referred to as phantom mode) wherein the injection in said twisted pairs is done in a differential manner. This generates a new path for the communication using the radiation produced by this mode. The present patent uses orthogonal multi-injections for creating new channels, so it does not affect this patent.
Finally, the publication “Submission to Working Group T1E1.4” (GDSL, Gigabit DSL, J. Cioffi et al., T1E1.4/2003-487R1) can also be related to the state of the art. In this publication, differential injections on twisted pairs using a conductor chosen as a reference for the return signal are used. As on previous occasions, this document does not affect the novelty or inventive step, because the method described in this patent is based on orthogonal multi-injection on N conductors, and not on differential injections, to increase the performance of the communications system.